1. Field of the Invention
This invention relates to a stapler for electrically stapling sheets of paper or other material, and more particularly to a stapler provided with a single staple driving unit capable of automatically inserting staples into one or more stapling portions of the sheets to be bound, which is incorporated in a sheet handling device such as a copying machine and printer to form a sheet-binding system.
2. Description of the Prior Art
There have been variety of sheet-binding systems incorporating a stapler capable of automatically stapling a sheaf of sheets of paper discharged from a sheet handling device such as various copying machines or printers. One of prior art staplers applicable for sheet binding has been proposed in U.S. Pat. No. 4,542,844 (corresp. to Japanese Patent Application Public Disclosure No. SHO 59(1984)-64279(A)). This conventional stapler enables staples to be continuously driven while being formed from short lengths of thin wires secured in a belt fashion with a single operation.
For instance, by making such a stapler being driven electrically and incorporated in a copying machine, it is possible to compose an electric sheet-binding device so as to automatically bind copied sheets discharged from the copying machine with one staple, in such a manner as described in U.S. Pat. No. 4,134,672 (corresp. to Japanese Pat. Appln. Pub. Discl. No. SHO 53-119047(A)) and Japanese Pat. Appln. Pub. Discl. No. SHO 61(1986)-9669(A).
The sheets of paper may potentially be bound by forcing two or more staples into stapling positions along one side edge including corners of the sheets at a time by use of a plurality of conventional powered staplers. That is, in order to automatically insert the staples into two or more stapling positions of the sheets to be bound, the staple driving units of the same number as the staples to be inserted into the sheets are required and immovably located at the stapling positions in the sheet-binding device. Thus, it has been impossible to change the stapling positions in accordance with the conditions of binding the sheets, the size of the sheets and so on.
Although the stapler as proposed in Japanese Pat. Appln. Pub. Discl. No. SHO 61(1986)-9669 copes with the size of the sheets to be bound, even this prior art stapler can staple only at a fixed stapling position of the sheets.
There has been a need for a changeable stapling device capable of stapling at one or more arbitrary stapling positions, that is, arbitrarily selecting one of four corners (corner binding), one or more points in one of four sides (one-side binding), and one or more points of the gutter center (center binding or doublespread binding) of the sheets. However, no such convenient stapler has been ever suggested.
A stapler composed of a number of staple driving units immovable fixed may possibly perform stapling at arbitrary binding positions tea certain extent, but installation of the plurality of fixed staple driving units adds to the size and complexity of the stapler, resulting in a large overall size of the system and renders the operation of the binding system difficult. Still more, from any prior art in this field, there has in no way been accomplished a stapler capable of forcing staples into any stapling positions of the sheets of paper by use of a single staple driving unit, e.g. arbitrarily performing the corner binding and one-side binding, much less the doublespread binding with only one staple driving unit.